1. Field of the Invention
This invention relates to a potting composition used for the embedment and protection of light-emitting semiconductor members and a light-emitting semiconductor device comprising a light-emitting semiconductor member embedded in the potting composition.
2. Background Art
Traditional light-emitting semiconductor devices such as light-emitting diodes (LED) are lamp-type light-emitting semiconductor devices in which a light-emitting semiconductor member is disposed on a lead electrode and encapsulated with a transparent resin to a cannonball shape as shown in FIG. 3. They are recently replaced by the xe2x80x9csurface mountxe2x80x9d type as a result of simplification of the mounting technology. Nowadays surface mounting light-emitting semiconductor devices as shown in FIGS. 1 and 2 become the mainstream.
In FIGS. 1 to 3, the device includes a housing 1 of glass fiber-reinforced epoxy resin, a light-emitting semiconductor member 2, lead electrodes 3 and 4, a die-bonding material 5, gold wires 6, and an encapsulant or potting composition 7.
While resin compositions are used for the embedment of light-emitting semiconductor members such as LED, it is required that the cured resin compositions be transparent. Then compositions comprising an epoxy resin such as a bisphenol A epoxy resin or alicyclic epoxy resin and an acid anhydride curing agent are generally used (see Japanese Patent No. 3,241,338 corresponding to JP-A 11-274571 and JP-A 7-025987).
However, these transparent epoxy resins have drawbacks including poor durability to moisture due to a high percent water absorption, poor durability to light due to a low transmittance of short wavelength light, and coloring due to photo-degradation.
Under the circumstances, resin compositions comprising an organic compound having at least two carbon-to-carbon double bonds (which are reactive with SiH groups) in a molecule, a silicon compound having at least two SiH groups in a molecule, and a hydrosilylating catalyst were proposed for the embedment and protection of optical semiconductor members (see JP-A 2002-327126 and JP-A 2002-338833).
Regrettably, such organic compounds undergo slow curing reaction, require a long time for curing, and produce substantial residual stresses. This necessitates the combined use of a thermoplastic resin having poor heat resistance or a hydrolyzable group-containing metal compound having poor storage stability. It was then proposed to use high-hardness silicone resins for the embedment and protection purposes (see JP-A 2002-314139 corresponding to US 2002-0145152 and JP-A 2002-314143 corresponding to US 2002-0190262).
The high-hardness silicone resins, however, are less adhesive. In an encased light-emitting semiconductor device comprising a light-emitting member disposed in a ceramic and/or plastic housing, wherein the housing interior is filled with a silicone resin, a problem arises in a thermal shock test between xe2x88x9240xc2x0 C. and 120xc2x0 C., that the silicone resin separates from the ceramic or plastic housing.
Another problem arises from the fact that optical crystals of various compound semiconductors used in light-emitting members, such as SiC, GaAs, GaP, GaAsP, GaAlAs, InAlGaP, InGaN, and GaN, have high refractive indices. If the refractive index of potting resin is low as in the case of dimethylsilicone resin, light is reflected at the interface between the potting resin and the optical crystal, resulting in a lower emission efficiency.
It is then proposed to add an antireflection film as a means of enhancing the outcoupling efficiency (see JP-A 2001-246236 and JP-A 2001-217467 corresponding to U.S. Pat. No. 6,614,172). The provision of an antireflection film undesirably adds preparation steps and increases the cost.
An object of the invention is to provide a light-emitting semiconductor potting composition having minimized internal stress, improved adhesion and high light transmittance, and a light-emitting semiconductor device having a high emission efficiency.
We have found that an addition reaction-curing silicone resin composition comprising a phenyl group-containing organopolysiloxane having a vinyl group at an end of its molecular chain as a base polymer and optionally, an organosilicon compound having a silicon atom-bonded alkoxy group possesses both low stress and transparency in the cured state and exhibits satisfactory adhesive properties. The present invention is predicated on this finding.
In one aspect, the present invention provides a light-emitting semiconductor potting composition comprising
(A) 100 parts by weight of an organopolysiloxane having a vinyl group at an end of its molecular chain, represented by the average compositional formula (1):
RaSiO(4xe2x88x92a)/2xe2x80x83xe2x80x83(1)
wherein R is a monovalent organic group, at least 5 mol % of R being phenyl, and xe2x80x9caxe2x80x9d is a number of 1.5 to 3.0,
(B) an organohydrogenpolysiloxane having at least two hydrogen atoms each directly bonded to a silicon atom in a molecule, represented by the average compositional formula (2):
R1bHcSiO(4xe2x88x92bxe2x88x92c)/2xe2x80x83xe2x80x83(2)
wherein R1 is a monovalent organic group, b is a positive number of 0.7 to 2.1, c is a positive number of 0.001 to 1.0, and the sum of b+c is 0.8 to 3, in an amount to give 0.7 to 10 silicon atom-bonded hydrogen atoms per vinyl group in component (A),
(C) a platinum group metal catalyst in an amount to give 1 to 1,000 ppm of platinum group metal based on the weight of components (A) and (B) combined, and
(D) 0 to 10 parts by weight of an organosilicon compound having an alkoxy group bonded to a silicon atom. The cured product of the composition should have a refractive index of 1.41 to 1.56 at 25xc2x0 C. and 589 nm (sodium D line).
In another aspect, the present invention provides a light-emitting semiconductor device comprising a ceramic and/or plastic housing defining an open interior and a light-emitting semiconductor member disposed in the housing; or a light-emitting semiconductor device comprising a ceramic and/or plastic housing defining an open interior and a light-emitting semiconductor member disposed on lead electrodes in the housing. In both the embodiments, the interior of the housing is filled with the potting composition in the cured state so that the semiconductor member is embedded in and protected with the cured composition.